Carbon dioxide composition



CARBON DIOXIDE COMPOSITION Application September '25, 1953 Serial No. 382,445

No Drawing.

8 Claims.

The present invention relates to carbon dioxide stored under pressure, and, more particularly, to carbon dioxide containing a material adapted to suppress the generation of electrostatic charges upon discharge thereof.

Carbon dioxide stored under pressure in liquid and] or gaseous state is widely used as a fire-extinguishingmedium by discharging the same through a .snow forming shield or horn for directing the carbon dioxide on thefire. One of such uses is in connection with portable fire extinguishers adapted to be carried by the operator to thelocation of the fire. Such extinguishers, as illustrated in United States Patent No. 1,760,274,, generally comprise a container having a discharge control valve and a snow forming horn connected to the outlet of the valve. The fluid carbon dioxide enters the horn through a nozzle or orifice at a high velocity and is expanded to produce a stream of carbon dioxide gas and snow particles in admixture.

It is well .known that the violent collision of carbon dioxide snow particles against each other andagainst the inner -wall of the horn generate electrostatic charges of considerable magnitude, and, that under conditions of relatively low humidity, these charges accumulate on the extinguisher which acts as sort of a condenser. Eventually, the charge "is released through the operator carrying the extinguisher with the result that the operator receives an'electric shock.

In United Sates Patent No. 2,785,124 it has been proposed 'to eliminate or to minimize the generation and accumulation of electrostatic charges in the foregoing manner by introducing into the carbon dioxide an oily material in an amount sufficient to provide a lubricating film on the surface of the snow particles and thereby greatly reduce friction upon collision of the particles against each other and against the inner wall of the horn. This method effected a substantial reduction in the charge generated but did not solve the problem completely. The operator still received a perceptible electric shock which, while not dangerous, caused fright and annoyance. Also, the oily material, in order to provide a sufficient lubricating effect, had to be used in such amounts that a visible film thereof remained on the inner wall of the horn and States Patent in the vicinity of the fire, thus giving the impression that the carbon dioxide contained a substance which was fiarnmable or was damaging to the goods it contacted. While such a film actually is not harmful or objectionable, it creates customer dissatisfaction and detracts from the sales appeal of the carbon dioxide composition.

Accordingly, an object of the present invention is to overcome the foregoing difficulties and objections in a simple, practical and economical manner.

Another object is to more completely suppress the generation of electrostatic charges in connection with carbon dioxide fire extinguishers.

Another object is to accomplish the foregoing by utilizing materials which can be used in extremely small amounts to effectively suppress the generation of electrostatic charges and are readily miscible with the carbon dioxide.

A further object is to utilize materials which do not leave objectionable films or deposits, particularly if used in small amounts.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In accordance with the invention, it has been found that these objects can be accomplished by providing fluid carbon dioxide stored under pressure containing a liquid non-volatile poly-alkyl ester in an amount suflicient to suppress the generation of electrostatic charges upon discharge of the carbon dioxide under pressure conditions whereby the carbon dioxide will be partially converted into snow particles. More particularly, it has been found that such poly-alkyl esters which are readily miscible with liquid carbon dioxide are particularly effective.

By the term poly-alkyl ester as used herein is meant a poly-hydrocar'byl ester, that is, a derivative of an acid obtained by the exchange of alkyl radicals for two or more replaceable hydrogen atoms wherein each alkyl radical is separately linked by an oxygen atom to a common or individual polyvalent ester nucleus. In some cases this nucleus has a double bonded oxygen atom linked thereto.

The term alkyl, in its general sense, includes monovalent aliphatic and aromatic hydrocarbon radicals. The aliphatic radicals, in particular, are termed alphyls; and the aromatic radicals, in particular, are termed aryls.

More specifically, the following additive materials, listed in Table I together with their chemical formulas, have been found capable of suppressing the generation of electros'tatic charges in the manner contemplated by the present invention. These materials are available in liquid form, are miscible with liquid carbon dioxide, and are not volatile within the usual range of atmospheric tempera tures.

Other materials, which are available in liquid form, are miscible with liquid carbon dioxide and are nonvolatile within the usual range of atmospheric temperatures, are listed in Table II. 3

Table II Additive material Butyl bcnzyl phthalate.

Butyl phthalyl butyl glycollatc.

Cresyl diphenyl phosphate.

Di (2-ethy1hexyl) adipate.

Di (2-ethylhexyl) phthalatc.

Di (2-ethylhexyl) tetrahydrophthalate. 2,-2 (2'ethylhexamido) diethyl di (2-ethylhcxoate). Ethyl phthalyl ethyl glycollate.

Methyl phthalyl ethyl glycollate. Polyethylene glycol di (2-ethylhexoatc). 'Iriethylene glycol di (2-ethylbutyrate). Triethylene glycol di (2-ethylhexoatc).

Tri (zethylehxyl) phosphate.

Tricrcsyl phosphate.

1 A mixture of materials, resembling triethylene glycol di (2-ethylhexoate) and having similar physical properties, sold by Carbide and Carbon Chemicals Company (see Flexol Plasticizcrs booklet, 1951, pages 28 to 31 inclusive).

The materials listed in Tables I and II have specific gravities ranging from about .92 to about 1.22, and are non-volatile in the sense that they are less volatile than water.

The carbon dioxide may be of the commercial grade available in liquid state or in solid blocks of so called Dry Ice adapted to be converted into liquid state. For example, commercially available liquid carbon dioxide having a purity between about 99.5% and 99.9% is preferred.

It has been found that the aforementioned additives will suppress the generation of electrostatic charges with some degree of effectiveness if present in amounts of about .0075% by weight. However, in order to take into account extreme conditions of low temperature and low relative humidity under which the fire extinguisher may be operated and the manner in which the additives are admixed with the carbon dioxide, it is recommended that between .01% and .2% by weight of these materials be present in the carbon dioxide. As a practical matter, the amounts of these materials should not exceed about 1% by weight, whereby to use the additives economically and to maintain the purity of the carbon dioxide as high as possible, although the presence of somewhat greater amounts does not adversely affect the suppression of electrostatic charges to some extent. Therefore, it may be said that the composition should contain at least .0075 by weight of one or several of the additive materials, and should not contain more than 1% by weight of the same.

The suppression of electrostatic generation in discharging carbon dioxide through a horn was demonstrated by utilizing apparatus comprising a slab of insulating material of the Bakelite type having a two inch thickness and a length and width to enable a fifteen pound carbon dioxide fire extinguisher (of the general type shown in United States Patent No. 2,562,963) to be supported thereon while leaving suflicient room for an operator to stand on the slab adjacent the extinguisher; a vacuum tube type voltmeter, having one side connected to the steel container of the fire extinguisher and having the other side grounded; and a resistor shunted across the meter to enable the latter to be used as an ammeter. The meter used was of the zero center type with plus and minus scales to enable reading either plus or minus electrostatic generation, and was electrically rated whereby the use of a one megohm resistor calibrated the units on the meter scales to read in microamperes.

Fifteen pound portable carbon dioxide fire extinguishers, first having a quantity of the additives poured therein, as indicated in Table III, and were charged with fifteen pounds of liquid carbon dioxide at about 70 F. In each instance, the extinguisher was placed on the insulating slab, the meter was connected to the ground and to the extinguisher in the manner just described, and the operator, while standing on the slab and insulated entirely from the ground, opened the extinguisher valve fully and permitted the contents of the extinguisher to be discharged completely therefrom. The meter was observed closely to determine whether or not there was any flow of current.

Table III Test percent by weight Additive material Observation Trimethyl borate 2 No needle deflection or perceptible vibration thereof.

Triethyl borate Tributyl borate.

Triamyl borate.

Methyl carbonate Do. Slight needle vibration.

HHHHHNNNNNNNNNNMNNNN 1 .1% by weight is equivalent to about 10 cc. or .34 fluid ounces in 15 pounds of liquid carbon dioxide.

A test was made with a composition having a tributyl phthalate content of about only .05% by weight, and slight deflection of the needle giving a reading of less than one microampere was observed. In order to demonstrate that such a trickle of current did not build up any charge on the extinguisher, the meter and resistor were disconnected, and one side of a spark gap was grounded and the other side was connected to the extinguisher through the operators hand. While discharging a charge of the aforementioned composition, the electrodes were brought together to reduce the gap gradually until finally the electrodes were in contact. At no time was a spark observed or was a shock felt by the operator, thereby demonstrating that the generation of a perceptible electrostatic charge was eliminated even with a very low additive content.

Fifteen pound portable carbon dioxide fire extinguishers, first having a quantity of the additives of Table II poured therein, as indicated in Table IV, and were charged with fifteen pounds of liquid carbon dioxide at about 70 F. These extinguishers then were discharged under the conditions referred to in connection with Table III.

Table IV Test I Content; No. Additive material percent Observation f by weight 22.-.. Butylbenzyl phthalate .05- Slight momentary needle deflection. 23-.-. Butyl phthalyl butyl gly- .05 Do.

; collate. 24.-.- Cresyl dlphenyl phosphate. .05 Do. 25.- Di (Zethylhexyl) adipate .05 Do. 26.--. Di (Z-ethylhexyl) phthalate. .05 Do. 27 D1 (2-ethylhexyl) tetrahy- .05 Do.

drophthalate. 28...- 2,-2 (z-ethylhexamido) di- .05 Do.

ethyl di (Z-ethylhexoate). 29..-. Egigl phthalyl ethyl glycol- .05 Do.

- e. 30..-- Metllilylc phthalyl ethyl gly- .05 Do.

co a e. 31 Polyethylene glycol di (2- .05 Slight momentary I ethylhexoate). needle vibration. 32..-. 'Iriethylene glycol di (2 .05 Slight momentary etln7lbutyrate). needle deflection. 33.... Triethylene glycol di (2- ..05 Slight momentary ethylhexoate). needle vibration. 34--.. Tri (2-ethylhexyl) phos- .05 Slight momentary p ate. needle deflection. 35..-- 'Iricresyl phosphate .05 Do.

A number of tests were made with the additive materials present in amounts between .03% and .035% by weight of the carbon dioxide composition, by pouring the same in the fire extinguisher, adding the carbon dioxide and then rocking and/or rolling the extinguisher to agitate the composition therein and thereby to promote better admixture of the additive materials with the carbon dioxide. Upon discharge of the contents under the conditions previously described herein, no needle deflection or perceptible needle vibration was observed.

Similar tests were made with compositions having between about .0075% and .015% of the additive materials blown or aerated into the liquid carbon dioxide, and again no needle deflection or perceptible vibration thereof was observed, thus indicating that thorough admixture .of the additive material reduces the quantity required to inhibit the generation of electrostatic charges.

A comparison 'test was made by discharging fifteen pounds of carbon dioxide without any of the additives, but under the same conditions just described. Sparks jumped the gap at one to two inches, and considerable shocks could be felt by the operator, thus demonstrating that carbon dioxide without an additive generates electrostatic'charges.

A second comparison test was made, but substituting the meter for the spark gap, and readings in excess of fifteen microamperes were observed, thus demonstrating an appreciable flow of current.

In all of the foregoing tests, the ambient temperature was about 70 F. at about 40% relative humidity.

Further tests were made at between and relative humidity with carbon dioxide compositions having .1% by weight of tributyl borate content and at temperatures as low as about minus F., and again the generation of electrostatic charges was effectively suppressed.

It has been found that the presence of Water in liquid carbon dioxide, even in small amounts, promotes the generation of electrostatic charges. In order to demonstrate this, about two cubic centimeters of water were added to fifteen pounds of carbon dioxide, and, upon discharge of this mass of carbon dioxide, a terrific electrostatic charge in a negative direction was developed.

This test was repeated but with ten cubic centimeters (.1% by weight) of dibutyl phthalate admixed with the carbon dioxide in addition to the water. This time, however, neither needle deflection was observed nor shock was felt, thereby demonstrating that the additives in accordance with the invention were capable of suppressing the generation of electrostatic charges even when the carbon dioxide contained added water. Thus, if grades of carbon dioxide having a higher water content than good commercial grades are used, the additives are effective to suppress the generation of electrostatic charges. '-In order to illustrate this, the last described test was repeated by adding about twelve cubic centimeters of a mixture of about equal volumes of water and dibutyl phthalate to the carbon dioxide. It was found that this mixture suppressed the generation of electrostatic charges to the same extent.

Further tests were made with mixtures of the additives listed in Tables I and II and water. Such mixtures comprised from about one to about two parts by weight of the additive and one part by weight of water, and between about .02% and about .05 by weight of such mixtures were admixed with the liquid carbon dioxide. It was found that these mixtures improved the static generation suppression action of each of the additives in that no needle vibration or deflection was observed in any case, produced more uniform results with very small quantities of the additives in the composition whereby any of the thirty additives are equally suitable without any preference to any particular additive, and thereby greatly simplified the selection of additives and optimum quantities in the compounding of the composition. These results were unexpected because water, when present in the composition in amounts sufiicien't to intensify the generationof electrostatic charges, actually rendered the additives more effective in suppressing such charges.

Since liquid carbon dioxide cannot exist in acontainer at a temperature above 87.8 F., its critical temperature, tests were made by discharging gaseous carbon dioxide having a temperature of about F. and containing about .1% by weight of dibutyl phthalate, and it was found that static was efiectively suppressed. This perhaps is due to the fact that upon initial discharge expansion takes place in the container which rapidly lowers the temperature of the gaseous carbon dioxide below its critical temperature to convert the same into its liquid state, whereby the miscibility of the additive in the carbon dioxide is reestablished.

In order to demonstrate that the composition can withstand sub-zero temperatures, a fifteen pound charge of carbon dioxide containing about .1% by weight of dibutyl phthalate was maintained at -40 F. for several hours and was discharged without the generation of electrostatic charges.

While it is not intended to attribute the electrostatic suppressing characteristics of the additives in accordance with the invention toany particular theory, it is likely that suppression is achieved along the following lines. As liquid carbon dioxide under pressure is released, it must cool and reach a definite critical density state when snow forms. At the zone in the path of discharge where this occurs, the carbon dioxide is in a metastable supersaturated state such that many thousands of crystals of carbon dioxide form at once which travel at a high velocity and in close proximity to each other. The most intensive generation of static would take place at this zone which most likely is within the horn. It is believed that the presence of the additive materials causes nucleation to promote the formation of crystals before or after normal transformation to snow, thereby relieving supersaturation and the usual high collision rate and the resulting electrostatic charge generation within the horn.

From the foregoing description, it will be seen that the present invent-ion provides a simple, practical and economical manner of effectively suppressing the generation of electrostatic charges upon discharging carbon dioxide through a snow forming horn or the like.

It will be understood that the details and examples hereinbefore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

This application is a continuationdn-part of application for United States Letters Patent, Serial No. 304,227, filed August 13, 1952, now abandoned.

I claim:

1. A fluid carbon dioxide composition stored under pressure consisting essentially of carbon dioxide and a material selected from the group consisting of trimethyl borate, triethyl borate, tributyl borate, triamyl borate, methyl carbonate, ethyl carbonate, propyl carbonate, diethyl oxalate, dibutyl oxalate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diamyl phthalate, butyl benzyl phthalate, butyl phthalyl butyl glycollate, cresyl diphenyl phosphate, di (2-ethylhexyl) adipate, di (2-ethylhexyl) phthalate, di (2-ethylhexyl) tetrahydrophthalate, 2,-2 (Z-ethylhexamido) diethyl di (2-ethylhexoate), ethyl phthalyl ethyl glycollate, methyl phthalyl ethyl glycollate, triethylene glycol di (Z-ethylbutyrate), triethylene glycol di (2-ethylhexoate), tri (Z-ethylhexyl) phosphate and tricresyl phosphate which are miscible with liquid carbon dioxide, said material being present in an amount suflicient to suppress the generation of electrostatic charges upon discharge of the carbon dioxide under pressure conditions whereby the carbon dioxide will be partially converted into snow particles.

2. Fluid carbon dioxide according to claim 1, containing between about .0075 and about 1% by weight of said material.

3. Fluid carbon dioxide according to claim 1, containing between .0075% and 2% by weight of said material.

4. Fluid carbon dioxide according to claim 1, containing approximately .05 by weight of said material.

5. Fluid carbon dioxide according to claim 1, containing approximately between .02% and .12% by weight of a mixture comprising about one part by weight of water and from about one to about five parts by weight of said material.

6. Fluid carbon dioxide according to claim 1, containing approximately between .02% and .05 by weight of a mixture comprising about one part by weight of water and from about one to about two parts by weight of said material.

7. The method of suppressing the generation of electrostatic charges upon discharge of fluid carbon dioxide under pressure conditions whereby the carbon dioxide will be partially converted into snow particles, which method consists of the step of controlling the crystal growth of the snow by the addition of between about .0075% and about 1% by weight of a non-volatile liquid material to the carbon dioxide which is miscible with carbon dioxide in its liquid state, said material being selected from the group consisting of trimethyl borate, triethyl borate, tributyl borate, triamyl borate, methyl carbonate, ethyl carbonate, propyl carbonate, diethyl oxalate, dibutyl oxalate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diamyl pthalate, butyl benzyl phthalate, butyl phthalyl butyl glycollate, cresyl diphenyl phosphate, d i(2- ethylhexyl)adipate, di(2 ethylhexyl)phthalate, di(2 ethylhexyl)tetrahydrophthalate, 2,2 (2-ethylhexamido) diethyl di(2-ethylhexoate), ethyl phthalyl ethyl glycollate, methyl phthalyl ethyl glycollate, triethylene glycol di(2 ethylbutyrate), triethylene glycol di(2-ethylhexoate), tri- (Z-ethylhexyl) phosphate and tricresyl phosphate.

8. The method of suppressing the generation of electrostatic charges upon discharge of fluid carbon dioxide under pressure conditions whereby the carbon dioxide will be partially converted into snow particles, which method consists of the step of controlling the crystal growth of the snow by the addition of between about .02% and about .12% by weight of a mixture comprising about one part by weight waterand from about one to about five parts by weight of a non-volatile liquid material to the carbon dioxide which is miscible with carbon dioxide in its liquid state, said material being selected from the group consisting of trimethyl borate, triethyl borate, tributyl borate, triamyl borate, methyl carbonate, ethyl carbonate, propyl carbonate, diethyl oxalate, dibutyl oxalate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diamyl phthalate, butyl benzyl phthalate, butyl phthalyl butyl glycollate, cresyl diphenyl phosphate, di (Z-ethylhexyl) adipate, di (2-ethylhexyl) phthalate, di (Z-ethylhexyl) tetrahydrophthalate, 2,-2' (2-ethylhexamido) diethyl di (2-ethylhexoate), ethyl phthalyl ethyl glycollate, methyl phthalyl ethyl glycollate, triethylene glycol di (2- ethylbutyrate), triethylene glycol di (2-ethylhexoate), tri (2ethy1hexyl) phosphate and tricresyl phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,321,023 Goodhue et a1. June 8, 1943 2,559,091 Reasenberg July 3, 1951 2,785,124 Grant Mar. 12, 1957 FOREIGN PATENTS 500,755 Belgium ...Feb. 15, 1951 

1. A FLUID CARBON DIOXIDE COMPOSITION STORED UNDER PRESSURE CONSISTING ESSENTIALLY OF CARBON DIOXIDE AND A MATERIAL SELECTED FROM THE GROUP CONSISTING OF TRIMETHYL BORATE, TRIETHYL BORATE, TRIBUTYL BORATE, TRIAMYL BORATE, METHYL CARBONATE, ETHYL CARBONATE, PROPYL CARBONATE, DIETHYL OXALATE, DIBUTYL OXALATE, TRIMETHYL PHOSPHATE, TRIETHYL PHOSPHATE, TRIBUTYL PHOSPHATE, DIMETHYL PHATHALATE, DIETHYL PHATHALATE, DIBUTYL PHATHALATE, DIMAYL PHALATE, BUTYL BENZLY PHTHALATE, BUTYL PHTHALYL BUTYL GLYCOLLATE, CRESYL DIPHENYL PHOSPHATE, DI (2-ETHYLHEXYL) ADIPATE, DI (2-ETHYLHEXYL) PHTHALATE, DI (2-ETHYLHEXYL) TETRAHYDROHEXOATE), ETHYL PHTHALYL ETHYL GLYCOLLATE, METHYL PHTHALYL HEXOATE)M ETHYL PHTHALYL ETHYL GLYCOLLATE, EMTHYL PHATHALYL ETHYL GYLCOLLATE, TRIETHYLENE GLYCOL DI (2-ETHYLBUTYRATE), TRIETHYLENE GLYCOL DI (2-ETHYLHEXOATE), TRI (2-ETHYLHEXYL) PHOSPHATE AND TRICRESYL PHOSPHATE WHICH ARE MISCIBLE WITH LIQUID CARBON DIOXIDE, SAID MATERIAL BEING PRESENT IN AN AMOUNT SUFFICIENT TO SUPPRESS THE GENERATION OF ELECTROSTATIC CHARGES UPON DISCHARGE OF THE CARBON DIOXIDE UNDER PRESSURE CONDITIONS WHEREBY THE CARBON DIOXIDE WILL BE PARTIALLY CONVERTED INTO SNOW PARTICLES. 